1. Field of the Invention
The present invention relates to a pattern matching and pattern recognition system which is applied to an application that demands different distance indexes, e.g., an artificial intelligence system, data bank system, Internet router, or mobile terminal (e.g., mobile videophone) to determine a pattern, of the reference patterns in a database, which is a most similar (nearest distance) to an input pattern, an associative memory apparatus used in the system, and a pattern matching and pattern recognition processing method.
2. Description of the Related Art
Pattern matching and pattern recognition are a basic function in many application fields developed in the information technology (IT) society, including network routers, codebook-based data compression, target recognition, and the like. In applications, in particular, different distance indexes may be advantageously used for necessary pattern recognition and pattern matching.
When pattern matching and pattern recognition are performed using various kinds of different distance indexes, a pattern exhibiting the largest similarity (nearest distance) with respect to an input pattern is determined from the reference patterns in a database. A proper distance index is selected in accordance with the type of pattern to be recognized. Among applications which have recently attracted a great deal of attention, and which demand short search times, and place importance on real-time performance, examples that have different distance indexes are video signal compression using vector quantization (Manhattan distance) [reference 1] and fingerprint recognition (Hamming distance) [references 2 and 3].
Reference 1: T. Nozawa et al., “A Parallel Vector-Quantization Processor Eliminating Redundant Calculations for Real-Time Motion Picture Compression”, IEEE J. Solid-State Circuits, vol. 35, pp. 1744–1751, 2000.
Reference 2: S. Jung et al., “A Low-Power and High-Performance CMOS Fingerprint Sensing and Encoding Architecture”, IEEE J. Solid-State Circuits, vol. 34, pp. 978–984, 1999.
Reference 3: S. Shigematsu et al., “A Single-Chip Fingerprint Sensor and Identifier”, IEEE J. Solid-State Circuits, vol. 34, pp. 1852–1859, 1999.
The adaptability of conventional pattern recognition systems with respect to different distance indexes currently depends on software, and there is currently no solution based on efficient hardware. Attention is being given to the implementation of efficient hardware as a useful technique because it can achieve practicality in a wide range.